Transcranial Direct Current Stimulation Therapy for Central Hypersomnia Without Cataplexy

Inclusion Criteria: * Age 18 - 70 years * Epworth Sleepiness scale score \>10 * Stable medication dosage over previous 4 weeks * Able to understand English and read and write at the 8th grade level and give a written informed consent document. * Stable sleep/wake schedule (that is, no rotating shift work) * Clinical diagnosis of any of the following: 1. Idiopathic Hypersomnia 2. Narcolepsy without Cataplexy 3. Hypersomnia in OSA patients adequately treated with PAP therapy or dental device 4. Posttraumatic hypersomnia 5. Hypersomnia, unspecified * Multiple sleep latency test (MSLT) shows fewer than two sleep onset REM periods and a mean sleep latency of ≤ 8 minutes. An MSLT is not required for inclusion of OSA patients provided their Epworth Sleepiness Scale (ESS) score is \>10. Adequately treated OSA patients will be defined as: i) an average PAP usage of \> 4 hours per night and a residual apnea-hypopnea index (AHI) of \<10/hour based on PAP machine download during at least a 30-day period, or ii) regular use of dental device during sleep based on self-report and a prior sleep study showing an AHI \<10/hour while using the dental device. * Subjects with idiopathic hypersomnia with an MSLT mean sleep latency of \> 8 minutes will be included provided they have hypersomnia symptoms and habitually long sleep times (average of \>10 hours per day) documented by actigraphy for at least 7 days.18 Exclusion Criteria: * Self-reported habitual sleep period of \< 7 hours/night * History of automobile accident due to falling asleep while driving * Currently taking stimulant medications such as Modafinil, Armodafinil, Methylphenidate, or Dextroamphetamnie. * Inability to understand or read English * Clear history of cataplexy * Moderate or severe sleep apnea defined as an apnea-hypopnea index (AHI) of \> 15/hour based on a previous sleep study and non-compliant with treatment. * Self-reported Substance abuse (current) * Excessive alcohol consumption defined as: * More than 3 glasses of wine a day * More than 3 beers a day * More than 60 mL of hard liquor a day * Presence of cardiac pacemaker or automatic implantable cardioverter-defibrillator (AICD). * Pregnancy, lactation * Recent hospitalization for major surgery/major illness (within past 1 month) * Non-removable metal or tattoos around head * Use of implantable birth control device such as Implanon * History of severe and frequent headaches * Known coronary artery disease * Seizure disorder * Uncontrolled hypertension * Congestive heart failure